Phase Locked Loop (PLL) circuits are well known and used for frequency control in a variety of applications. For example, they can be configured as frequency multipliers, demodulators, tracking generators or clock recovery circuits. A typical PLL circuit has a loop filter to filter out high frequency components such as spurs generated by a phase comparator or a charge pump in the PLL circuit. A typical loop filter uses passive components such as capacitors and resistors to filter out any undesired signals such as spurs. However, a typical loop filter requires high capacitance capacitor(s) to filter out high frequency components such as spurs. Since high capacitance capacitors occupy large amount of space in integrated circuits, the high capacitance capacitors could not be integrated into integrated circuits that include PLL circuits. As a result, the loop filters were usually located outside of the integrated circuits.
To solve the above problem with loop filters, a dual path loop filter was designed to allow loop filters to be integrated into IC circuits. The dual path loop filter uses active circuit components such as op-amps to filter out unwanted signals. However, active circuit components create additional noise and consume more power than passive circuit components.
Therefore, there is a need in the art for a new type of dual path loop filter design that can ameliorate the shortcomings of previous loop filter designs.